[vtkusers] contouring point data

burlen burlen at apollo.sr.unh.edu
Thu Jul 26 15:19:06 EDT 2007

In case you didn't realize this, many vtk filters require both point 
data and cells(the other repsonses didn't specifically point this out). 
Contour filter requires both point data and cell geometry because it 
needs cell geometry to compute interpolation on faces of a cell and so 
it knows what cell to continue the generation process in once the 
contour reaches the edge of a cell. It needs to know how the data is 
connected. As the other reply suggested one way you could construct the 
required geometry from a point set is to pass that data through a 
delaunay filter, how ever this would be very slow if you have a lot of 
points in 3 space. Maybe you already have the geometry somewhere?? If so 
you should construct cells for your unstructured grid.

Erik Anderson wrote:
> Hi all,
>     I have been trying to get iso-contours generated for point data 
> for a while now with no luck.  Any help anyone can give would be much 
> appreciated.  Below is a more complete description of the problem:
> I have a vtkUnstructuredGrid that is storing point data. In other 
> words, every vertex in the dataset is a discrete point to be 
> rendered.  Each point has several data arrays associated with it to be 
> used for coloring, scaling, etc operations during glyph rendering.  I 
> now want to generate isosurfaces for these data, but I cannot figure 
> out how to do something like this from within VTK.
> One method that I can loosely translate into VTK language (but which 
> I've had no success getting a pipeline working with) would be as follows:
> embed the point set in a structured grid
> for each vertex in the grid:
>    evaluate an implicit function (meta-ball like function)
> apply marching cubes or other isosurface extraction technique
> render surface
> The problem with the above approach is that I have been unable to 
> construct a pipeline that would evaluate a function taking input from 
> each point in the dataset.
> Any help would be greatly appreciated!
> Thank you,
> Erik Anderson
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Burlen Loring
Information Technologist III
Space Science Center
Institute for the Study of Earth, Oceans, and Space
University of New Hampshire
39 College Road, Durham, NH 03824
Phone: 603-862-1140

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